The invention relates generally to wellhead casing assemblies. In particular, the invention relates to a wellhead casing assembly having a casing hanger actuated by a contractible ring disposed in a wellhead housing.
Casing is strong steel pipe that is used in an oil and gas well to ensure a pressure-tight connection from the surface to the oil and/or gas reservoir. Casing serves many purposes in the well. It can protect the wellbore from caving in or being washed out. It can also confine production to the wellbore; so that water does not intrude into the wellbore or drilling mud intrude into the surrounding formations. It can also provide an anchor for the components of the well. Production tubing, such as coiled tubing, typically is used to transport oil to the surface.
Several sections of casing joined together end-to-end are known as a “casing string.” Because casing serves several different purposes, it is typical to install more than casing string in a well. Casing strings typically are run in a concentric arrangement with each inner casing string extending progressively deeper into the ground. For example, typically, the outermost casing string extends to the shallowest depth in the ground and the innermost casing string extends to the deepest depth.
A casing hanger is a device that is used to support a casing string from a wellhead housing or other structure within the well. In addition, the casing hanger serves to ensure that the casing is properly located in the well. When the casing string has been run into the wellbore, the casing string is hung, or suspended, in the well by the casing hanger. Multiple casing hangers may supported by the wellhead housing.
Typically, the casing hanger rests on a landing shoulder inside the wellhead housing. In one type of wellhead housing, the load shoulder is permanently formed in the bore during manufacturing. This permanent load shoulder reduces the effective diameter for objects that are desired to be inserted in the wellbore below the casing hanger. For example, it may be desired to suspend one or more casing hangers from casing below the wellhead housing. In some instances, it may be desired that the casing hangers suspended below the wellhead housing take advantage of the full bore of the casing below the wellhead housing for the entire length of the bore.
A number of techniques have been developed to enable full bore access to components below the wellhead housing. However, these techniques typically use complicated load ring systems to support the casing hanger within the wellhead housing.
Therefore, an improved technique for supporting casing with a wellhead is desired. In particular, an improved technique for supporting a casing hanger in a wellhead while providing full bore access below the wellhead is desired.